Big Finish’s monthly range has been releasing a 2-CD full-cast Doctor Who story every month for fifteen years. That is quite a lot of Doctor Who. The prices are tiered by release date, and the first 50 releases are the lowest-priced, so it makes sense to start near the beginning until you know that you want to go deeper and spend more money.

I’m going to give my opinions on Big Finish’s monthly series, starting from the beginning. In this article, I’ll present my opinions of the earliest ten that I’ve listened to (not the earliest ten ever, since my own listening is not thorough).

I’m going to try to use a consistent grading scale. I’m using the grades I assigned in the freebies article as a baseline, and my grading scale is approximately as follows:
A: I find it exceptional, and I expect that most people will agree it is good.
B: I see no noteworthy flaws in it, or every flaw I see is balanced by a virtue, but it is not exceptionally excellent.
C: The story can be followed and has some worthwhile moments, but I would agree that it its flaws are significant or that it doesn’t necessarily warrant the length of its running time.
D: It actively resisted my attempts to enjoy it, and I expect most people will agree it is not worthwhile.
F: It is bad enough to be worth listening to specifically because it is bad.

I am also using a scale of continuity significance categories:
“Essential”: Later stories expect you to already know about this one before you start them, and listening to this one as homework is worthwhile.
“Optional”: Things from this story come up again, but to the best of my knowledge they are inessential where they appear, or they come with adequate recapping, or the quality of the later stories is too low to justify a homework assignment.
“None that I know of”: As far as I know, nothing comes up again, other than possibly in throwaway lines.
“Negative”: Something significant is contradicted later, or is left unaddressed in later situations where I would have expected it to be addressed.
The Sirens of Time
WHO’S IN IT: The Fifth, Sixth, and Seventh Doctors
THE SETTING: Multiple locations in time and space, culminating on Gallifrey.
THE VILLAINS: If you listen at all, I suggest listening without plot spoilers.
WHAT’S ITS DEAL: For their first Doctor Who release, Big Finish created a sort of sampler-pack story. The three Doctors featured have seemingly separate one-episode adventures, then team up for a shared climax.
THE CASE FOR: This is the first thing Big Finish released with the official BBC Doctor Who license, so it’s a logical starting point for completists. Between the separate episodes, you’re likely to enjoy one part or another.
THE CASE AGAINST: The story is disjointed, and the climax is too rushed for either a satisfying resolution or much fun multi-Doctor interaction.
THE MOOD: Completely separate moods for each of the four episodes.
HUMOR: Occasional witticisms and inter-Doctor banter.
CONTINUITY SIGNIFICANCE: Optional. The villains return later, sort of, but not in a way that depends on this story.
GRADE: C. Aside from being the first one and a multi-Doctor one, this isn’t especially recommendable.

Phantasmagoria
WHO’S IN IT: The Fifth Doctor and Turlough.
THE SETTING: Historical England.
THE VILLAIN: A mysterious nobleman and an army of ghosts.
WHAT’S ITS DEAL: This is Big Finish’s first Doctor Who ghost story. Like most Doctor Who ghost stories, the Doctor takes time to explain that ghosts don’t exist, then explain what is happening using science-fiction terminology that amounts to ghosts existing.
THE CASE FOR: Both the historical aspect and the horror aspect are well-done.
THE CASE AGAINST: There are some scenes where things happen in vague sound effects, the characters see them happening, and no one says out loud what they saw until later. One plot twist towards the end seems to exist only to have an extra plot twist.
THE MOOD: Fools make deals with powers beyond human understanding.
HUMOR: Not particularly.
CONTINUITY SIGNIFICANCE: None that I know of.
GRADE: C. Big Finish hadn’t yet found their feet yet, pacing-wise, but the core of a good script is visible nonetheless.

Whispers of Terror
WHO’S IN IT: The Sixth Doctor and Peri.
THE SETTING: A museum in the future.
THE VILLAINS: I suggest listening without plot spoilers.
WHAT’S ITS DEAL: Another ghost story, but with a locked-room mystery aspect and an especially science-fiction sort of ghost.
THE CASE FOR: The sci-fi is so soft as to be outright funny. Interesting use of the audio medium, with a story centered around the malicious editing of audio recordings. Colin Baker hams it up in an appropriate, entertaining way.
THE CASE AGAINST: This story seems to be taking place at a time well before the Sixth Doctor stopped being an asshole to Peri, which may be a turn-off. The very last scene seems to be thrown in for pointless shock value, and undermines some of what comes before.
THE MOOD: Political conspiracy, detective work, and a haunting, all neatly intertwined.
HUMOR: Sixth Doctor hammery and jokey science.
CONTINUITY SIGNIFICANCE: None that I know of.
GRADE: B. This is the first generally worthwhile Big Finish release. Listen unless you are averse to the asshole version of the Sixth Doctor.

Land of the Dead
WHO’S IN IT: The Fifth Doctor and Nyssa.
THE SETTING: Near-future Alaska.
THE VILLAINS: Living fossils, more or less.
WHAT’S ITS DEAL: Sort of a mummy’s-curse story, with paleontology instead of archeology
THE CASE FOR: The monsters are interesting on paper. If you’re a Nyssa completist, this is her first Big Finish appearance, and she’s handled pretty adequately as a character.
THE CASE AGAINST: Dreadful pacing, full of padding. Stereotyped Native Americans. Character motivations are cardboard-ish, but not in a fun farcical way.
THE MOOD: In the vastness of nature, mankind has dug too deep and discovered something terrible, but let’s listen to a Native American stock character lecture us about ecology for a while instead of looking at it.
HUMOR: Occasional moments of banter that do not work.
CONTINUITY SIGNIFICANCE: None that I know of.
GRADE: D. This is Big Finish’s first outright dud.

[Land of the Dead is followed by The Fearmonger, which I have not yet listened to.]

The Marian Conspiracy
WHO’S IN IT: The Sixth Doctor and Evelyn (audio-original; first appearance)
THE SETTING: Historical England.
THE VILLAINS: None in a conventional Doctor Who sense of villainy.
WHAT’S ITS DEAL: Big Finish’s first stab at what Doctor Who fans sometimes call a “pure historical”. Once the Doctor and Evelyn go to the past, the only supernatural or science-fiction elements in the story are what they’ve brought into the past with them.
THE CASE FOR: Evelyn has many characterization moments, and differs from other Sixth Doctor companions in major ways. There are enough factions and conspiracies in the past to keep things interesting.
THE CASE AGAINST: The story starts with a science fiction plot hook which it resolves in the end, but never fully explains.
THE MOOD: Religious and political factionalism, a Queen at risk of assassination, and no clear right or wrong side.
HUMOR: Evelyn has many fish-out-of-water scenes.
CONTINUITY SIGNIFICANCE: Optional. The exact circumstances of Evelyn joining up with the Doctor aren’t essential to her later adventures.
GRADE: B. If you’re interested either in Evelyn or in “pure historical” Doctor Who, you should get this one.

[The Marian Conspiracy is followed by The Genocide Machine, which I have not yet listened to.]
[The Genocide Machine is followed by Red Dawn, which I have not yet listened to.]
[Red Dawn is followed by The Spectre of Lanyon Moor, which I have not yet listened to.]
[The Spectre of Lanyon Moor is followed by Winter for the Adept, which I have not yet listened to.]

The Apocalypse Element
WHO’S IN IT: The Sixth Doctor and Evelyn
THE SETTING: Multiple planets in the future, including Gallifrey.
THE VILLAINS: Daleks.
WHAT’S ITS DEAL: This is part of Big Finish’s “Dalek Empire” arc, in which Daleks have a variety of more ambitious, complex plans than their typical military invasions.
THE CASE FOR: The stakes are high in an engaging way. Pacing is good. The Gallifrey portion of the story is interesting. Similarities to the later Time War are probably not wholly coincidental.
THE CASE AGAINST: The resolution involves a lot of particularly dubious technobabble. The tone is unusually dark for a Sixth Doctor story.
THE MOOD: The Daleks have Gallifrey and the Doctor thoroughly outfoxed, and survival is a matter of desperate gambles.
HUMOR: A few witticisms, but the story is largely too dark to sustain humor.
CONTINUITY SIGNIFICANCE: Optional. The resolution of this story contributes to later “Dalek Empire” incidents, but the details of how it plays out aren’t important to them.
GRADE: C. If you like very dark stories about Dalek invasions, bump it up to B.

[The Apocalypse Element is followed by The Fires of Vulcan, which I have not yet listened to.]
[The Fires of Vulcan is followed by The Shadow of the Scourge, which I have not yet listened to.]

The Holy Terror
WHO’S IN IT: The Sixth Doctor and Frobisher (a usually penguin-shaped shapeshifting companion of the Doctor from Doctor Who Magazine comics)
THE SETTING: Seemingly an Earth-analogue medieval kingdom, but it becomes obvious early on that this is not the case.
THE VILLAINS: None in a conventional Doctor Who sense of villainy.
WHAT’S ITS DEAL: This is writer Rob Shearman’s first contribution to Doctor Who, and like much of his other work it is more like an experimental stage play than a Doctor Who story.
THE CASE FOR: Fun dialogue and an intriguing setting. If you like Frobisher, this is the first of his two Big Finish appearances. The science fiction elements are used in a more dreamlike, less mechanistic way than typical Doctor Who, and used well in that regard.
THE CASE AGAINST: The Doctor and Frobisher are almost just visiting a plotline that would be happening anyway without them and doesn’t really have a place for them.
THE MOOD: Everyone is going mad in their own way at their own pace.
HUMOR: Constant well-executed black comedy.
CONTINUITY SIGNIFICANCE: None that I know of. Possibly negative, since there’s no simple way to line up the timeline of Doctor Who Magazine comics with the timeline of Big Finish audios.
GRADE: A. If you are comfortable with stories that wouldn’t have happened on television, then just go ahead and listen to this one as soon as you’re able to.

[The Holy Terror is followed by the unabridged version of The Mutant Phase, which I have not yet listened to in that version.]

Storm Warning
WHO’S IN IT: The Eighth Doctor and Charley (audio-original; first appearance)
THE SETTING: Historical Earth, mostly on a zeppelin over Europe.
THE VILLAINS: I suggest listening without plot spoilers.
WHAT’S ITS DEAL: Paul McGann signed on with Big Finish later than the Fifth through Seventh Doctors, and since he only had one television appearance, Big Finish had a virtual blank canvas for him starting with this story.
THE CASE FOR: As far as Big Finish audios are concerned, the Eighth Doctor is every bit as legitimate an incarnation as the others, and this is where you get in on the ground floor for him. Both the historical and science-fiction elements are well-done, and the parts where they come together have a sense of wonder and drama.
THE CASE AGAINST: Some background characters make decisions for no better reason than that the plot needs them to. The turn from nearly pure historical to heavy science-fiction is abrupt.
THE MOOD: In many different ways, this story is about the wonder of new beginnings.
HUMOR: Charley and the Doctor have a good quantity of banter.
CONTINUITY SIGNIFICANCE: Essential. A long-running plot thread starts here that is important to many subsequent Eighth Doctor and Charley stories, and not all of those stories recap this one. Thematically, the fallout from this story continues even into non-Charley Eighth Doctor stories.
GRADE: A. Big Finish’s Eighth Doctor era hits the ground running, and the story is worthwhile even aside from its value as an introduction.

Sword of Orion
WHO’S IN IT: The Eighth Doctor and Charley
THE SETTING: Spaceships in the future.
THE VILLAINS: Cybermen.
WHAT’S ITS DEAL: Charley’s first story as a confirmed companion of the Doctor, and her first encounter with a recurring Doctor Who nemesis.
THE CASE FOR: Tension is high. Even minor characters seem to have their own lives that extend outside this one story. The Cybermen are adapted to audio effectively.
THE CASE AGAINST: Some information is withheld and then revealed in ways that only make sense for suspense and not for actual narrative logic. The story is constructed from stock trope building blocks and Blade Runner fanfiction.
THE MOOD: Danger could be hiding anywhere on the ship, and there is no escape. Sort of vaguely like Alien.
HUMOR: Some comic relief moments, but largely just as setup for later horror moments.
CONTINUITY SIGNIFICANCE: Optional. This story introduces the Orion War, but the Orion War is generic enough to pick up from context when it appears later.
GRADE: C. An entirely competent horror-in-space story with few traces of originality.

The Stones of Venice
WHO’S IN IT: The Eighth Doctor and Charley
THE SETTING: Future Venice.
THE VILLAINS: Decadent aristocrats.
WHAT’S ITS DEAL: Charley’s first visit to Earth’s future, particularly to a time of quasi-apocalyptic decline.
THE CASE FOR: The setting is emotionally dramatic in a way that most Doctor Who settings aren’t.
THE CASE AGAINST: The story involves a lot of traveling back and forth around the city picking up pieces of information, with relatively little problem-solving or interesting conflict.
THE MOOD: Those who have stayed behind as the city sinks are mad or beyond hope, but there is still beauty to be prized.
HUMOR: There’s a bit of satire in the setting, but not focused enough to really call any of it comedic.
CONTINUITY SIGNIFICANCE: None that I know of.
GRADE: C. A lovely frame for a story, but not much of a story.